Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$121.37	10.830%	$134.5144	$134.51	$134.50	$134.50
Purchase #2	$58.36	9.841%	$64.1032	$64.10	$64.10	$64.10
Purchase #3	$242.48	12.499%	$272.7876	$272.79	$272.80	$272.80
Purchase #4	$196.70	7.702%	$211.8498	$211.85	$211.85	$211.80
Purchase #5	$181.86	12.531%	$204.6489	$204.65	$204.65	$204.60
Purchase #6	$100.48	11.382%	$111.9166	$111.92	$111.90	$111.90
Purchase #7	$139.36	3.688%	$144.4996	$144.50	$144.50	$144.50
7 purchase totals =	$1,040.61		$1,144.3201	$1,144.32	$1,144.30	$1,144.20